gps10MHzPortFrequencySource is a read-write pointer-type setting that lets an administrator specify which internal frequency source feeds this GPS 10MHz port's output. This is how an operator directs the chassis to distribute a particular internal clock (rather than a fixed default) out through this specific 10MHz output port. For example, an operator wanting this port to output the frequency derived from the currently-selected system reference clock would point this object at that clock's MIB object rather than at some other candidate source.